It is known that mixing apparatuses are widespread. In particular, in the field of cleaning and disinfection of surfaces, such apparatuses allow both treatment exclusively with water and adding of concentrated chemical products, such as for instance disinfectants, soaps, wet foams and dry foams. The apparatus described in document U.S. Pat. No. 7,017,621 B2 and the apparatus called KP1H available from the US company Knight are two examples of such mixing apparatuses.
With reference to FIG. 1, it may be observed that the hydraulic circuit of such apparatuses draws the water from the supply through a hydraulic cross connection 1, capable to operate with water pressure values up to 10 bars (i.e. 106 Pascals), controlled by a magnetically actuated valve 2. The hydraulic cross connection 1, the housing case (not shown in FIG. 1) of which is mounted on the wall (directly or through a bracket) so that the magnetically actuated valve 2 is frontally accessible by an operator, comprises an inlet duct 70 upstream of the valve 2, for connecting to the supply through a connector 74, and an outlet duct 71 allowing the connection to a hydraulic cross connection of another mixing apparatus (or to any other duct) connected downstream of that shown in FIG. 1 through a similar connector (not shown in FIG. 1). In the case where the outlet duct 71 is not connected to any downstream hydraulic cross connection (or any other duct), it is closed through a stopper 72. The connector 74 and the stopper 72 are attached to the inlet duct 70 and outlet duct 71, respectively, through corresponding quick coupling removable hooks 73 frontally applied (i.e. from the same side of the magnetically actuated valve 2) by an operator.
The hydraulic cross connection 1, downstream of the magnetically actuated valve 2, comprises an elbow 10 (formed by an upstream duct 21 and a downstream duct 22) downstream of which an assembly 3 of separation valves is present, for preventing the backflow towards the chemical products supply, and, downstream of these, a mixing device 4 based on the Venturi effect, that mixes the water with the chemical product. In particular, the mixing device 4 comprises a small tube 5 wherein, upon the passage of water, a low pressure and hence an aspiration of the chemical product from an aspiration tube 6 (connected to an external tank through a mouth 82) and its dilution in water are generated. Dosage depends on the flow rate and water pressure, and it is possible to manage the dilution through proper nozzles 7 which are inserted into external tubes (not shown) for aspirating the chemical product and which adjust the percentage thereof. Such apparatuses are completely automatic and, since they are constituted only by a hydraulic system, they do not need any power supply.
The presence of the assembly 3 of separation valves is necessary because the chemical product tank are connected to the water supply of drinking water, and backflow prevention of the chemical products towards the supply must be hence guaranteed, e.g. in the case where a temporary low pressure occurs in the supply. Some prior art separation valves are described, e.g., by documents EP 1 522 353 A1, U.S. Pat. No. 6,478,047 and U.S. Pat. No. 6,021,805.
The regulations of many countries require the presence of separation valves for guaranteeing the non-contamination of the supplies with the chemical products. In Europe, the types of valves are described by DIN EN 1717 regulation, and the separation valve assemblies generally comprise, as for the apparatus shown in FIG. 1, two cascaded valves: a flexible membrane separation valve 8, and an air gap valve 9 (wherein the flow of the liquid coming from the supply carries out a physical jump for entering the circuit comprising the mixing device 4). Examples of such two valves are the Flex-Gap™ and Aire-Gap™ valves available from the US company Knight.
With reference to FIG. 2, it may be observed that the flexible membrane separation valve comprises a housing 2020 with cylindrical symmetry, the lateral surfaces of which are provided with slits 2021, within which housing 2020 a hollow flexible membrane 2022 with cylindrical symmetry is housed, within which an insert 2023 with substantially cylindrical symmetry is in turn housed. The slits 2021 of the housing 2020 make the valve operate as an open system in air, preventing the mixed liquid from possibly rising back and contaminating the supply in case of a low pressure in the same supply. When the water flows in the mixing apparatus from the supply to the mixing device 4, it passes between the insert 2023 and the flexible membrane 2022, causing the latter to widen due to the pressure thus closing the passages of the slits 2021 of the housing 2020 outwards, modifying the operation of the valve that thus operates as a closed system. In this regard, it must be considered that some features of the flexible membrane separation valve only shown in FIGS. 1 and 2 and not described are actually not known in the prior art, as far as the inventors are aware, rather they are part of the flexible membrane separation valve according to the invention. He features which, though shown in FIGS. 1 and 2, are not known in the prior art will be expressly mentioned later with reference to FIG. 3.
However, the flexible membrane separation valves of the prior art suffer from some drawbacks, mainly due to the fact that they introduce a significant discontinuity in the flow of the water (e.g. in case of a mixing apparatus, from the water supply to the mixing device 4). First of all, the valve tightness is not perfect, most of all when the water starts to flow or at low operation pressures. Moreover, the effective flow rate of the valve is lower than its nominal value. Finally, in case of a mixing apparatus, the subsequent mixing device 4 has significant priming problems most of all at low operation pressures. Also, in the case where a plurality of chemical products can be mixed, there is the risk that the latter get in contact with each other before being diluted in water.